Appliance theft alarm using voltage magnitude switch

ABSTRACT

A theft alarm system which operates in conjunction with a signal distribution system for protecting a plurality of devices. The devices receive a signal which is distributed from a central signal location by a plurality of coaxial cable distribution lines extending between the central signal location and termination points. A continuous loop of coaxial cable is threaded through each of the devices and spliced to the respective coaxial cable distribution line. A voltage is applied to each coaxial cable distribution line at its termination point. Voltage sensing switches adjacent the central signal location sense open-circuiting or short-circuiting of any of the continuous coaxial cable loops and actuate a theft alarm.

United States Patent 1 8 Daniel Oct. 3, 1972 [54] APPLIANCE THEFT ALARM USING 3,457,560 7/1969 McKinley ..340/248 C VOLTAGE MAGNITUDE SWITCH 3,427,607 2/ 1969 Oesterle ..340/248 A [72] Inventor: Kenneth D. Daniel, Palo Alto, Calif. Primary Examiner john w. C a1 dwell 1 Assignee: Video g g, -s u y Assistant ExaminerWilliam M. Wannisky Calif- Attorney-Flehr, Hohbach, Test, Albritton & Herbert 22 F1 d: A 11 197 1 :2 57 ABSTRACT 21 N ,9 1 pp 0 A theft alarm system which operates in COIijLll'lCIlOl'l with a signal distribution system for protecting a plu- [52] [1.8. Cl. 340/256, l, alit f d vices The devices receive a which is 328/147, 324/98 distributed from a central signal location by a plurality Int. Cl. ..G08b 13/00 of coaxial cable distribution lines extending between [58] Fleld of Search" 340/280 248 248 the central signal location and termination points. A 340/248 317/29 R, 3 32; 307/130; continuous loop of coaxial cable is threaded through 325/308 309; 324/98; 328/ each of the devices and spliced to the respective coaxial cable distribution line. A voltage is applied to each References C'ted coaxial cable distribution line at its termination point. UNITED STATES PATENTS Voltage sensing switches adjacent the central signal location sense open-circuitmg or short-circuitmg of Sllman any of the continuous coaxial cable loops and actuate 3,553,673 1/1971 Fistell ..340/280 a th ft alarm 3,407,400 /1968 Lurie ..340/280 7 Claims, 4 Drawing Figures ;F F \7s -27 1 2 |5 24 I zz I VOLTA E SENS/:6 swim I ANTENNA II ,7. 5;;- l

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| 25 24 2: I-ev I VOLTAGE I r savsnve I Z I SWITCH ANTENNA ll I I l SIG/VflL SPL ITTER I T? I xv. sl ir I VOLTAGE SELECTIVE DETECTOR VOLTAGE SENSING SWITCH KENNETH D. DAM/EL INVENI'OE BACKGROUND OF THE INVENTION This invention pertains to a signal distribution system and more particularly pertains to a theft alarm system for protecting a plurality of devices which system operates in conjunction with a signal distribution system for the devices.

Almost every hotel and motel has a television set provided in each of its guest rooms. Typically there is a single antenna at a central location for receiving television signals and the received television signals are distributed (and amplified as might be required) to the television sets in the plurality of guest rooms. A typical distribution system for distributing the signals is a 75 ohm coaxial cable transmission line.

The incidence of theft of television sets from such hotels or motels has in some instances grown to alarming proportions. Present day television sets are readily carried by one person and guest are usually free to go to and from their rooms without having to pass by or through a lobby or registration office. This makes theft of such television sets an easy matter. Therefore, what is needed is a theft alarm system for notifying the hotel or motel management that one of the guests is attempting to steal a television set so that the police or other proper authorities may be rapidly notified. Further, such a theft alarm system should require a minimum of special wiring so that it may be inexpensively installed in a new structures or in existing structures.

BRIEF SUMMARY OF THE INVENTION Accordingly, it is object of this invention to provide a theft alarm system for protecting a plurality of devices from theft.

It is a more specific object of this invention to provide a theft alarm system which utilizes a signal distribution system to provide an alarm at a central location in response to attempted theft of any of a plurality of remote devices connected to the signal distribution system v Briefly, in accordance with one embodiment of the invention, a theft alarm system utilizes a signal distribution system for distributing signals to a plurality of devices. The signal distribution system typically includes a central signal location, a plurality of remote devices, each having a signal input, and a coaxial cable distribution system having a plurality of coaxial cable distribution lines, each extending between the central signal location and a termination point with the signal inputs of a portion of the plurality of devices connected to each of the coaxial cable distribution lines. The theft alarm system includes a continuous loop of coaxial tribution line. A voltage source is attached to the termination point of each of the distribution lines and applies a voltage to each of the distribution lines. A voltage sensing switch is interposed in each of the coaxial cable distribution lines between the devices and the central signal location. The voltage sensing switch is adapted to actuate an alarm when the voltage from a distribution lines termination point is no longer present at the voltage sensing switch. This condition corresponds to either an open circuit or short circuit of one of the continuous loops of coaxial cable which extend through the devices.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of the theft alarm system of this invention showing the manner in which the various portions are interconnected.

FIG. 2 is an illustrative diagram showing the manner in which continuous loops of coaxial cable are looped through devices to be protected and are spliced into a coaxial cable distribution line.

FIG. 3 is a detailed circuit diagram of the voltage sensing switches of FIG. 1.

FIG. 4 is a detailed circuit diagram of the voltage selective detector shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a system diagram of a theft alarm in accordance with this invention.

A signal such as an RF television signal, for example, is received by an antenna 11 and transmitted over a coaxial cable 12 to an RF/DC splitter 13. The RF/DC splitter 13 comprises a capacitor 14 for coupling the RF on coaxial cable 12 to a coaxial cable 15 and a RF choke 16 for blocking the RF television signal from a conductor 17 to which is connected a voltage selective detector 18. i

The coaxial cable 15 forms the input to a voltage passing TV signal splitter 19. The splitter 19 may be any of the many commercial or standard types available and functions to divide the television RF signal on the coaxial cable 15 into a plurality of signals on coaxial cables 20 and 21. Although only two coaxial cables 20 and 21 are shown at the output of the splitter 19, it is to be understood that be more outputs from the splitter 19 or multiple splitters may be provided for dividing the RF television signal on coaxial cable 15 into a plurality of outputs for application to a plurality of coaxial cables.

The coaxial cable 20 forms the input to a looped signal distribution system 22 and the coaxial cable 21 forms the input to a looped signal distribution system 23. It is to be understood that there may be more then two looped signal distribution systems, depending upon the number of hotel or motel rooms and devices which are to be protected.

The looped signal distribution system 22 comprises a voltage sensing switch 24 to which the coaxial cable 20 is connected. Also connected to the voltage sensing switch 24 are coaxial cables 25 and 26. The coaxial cable 25 extends through a plurality of devices 27, which may be television sets for example, to a termination arrangement 28. Similarly, the coaxial cable 26 extends through a plurality of television sets 27 and terminates in a termination arrangement 29. Typically, the voltage sensing switch 24 may be contained in a laundry closet or the like at the end of a hallway of rooms in a motel or hotel. Coaxial cable 25 may extend from the laundry closet through the television sets 27 on one side of the hallway and the coaxial cable 26 may extend through the television sets 27 in the rooms on the opposite side of the hallway. The termination arrangements 28 and 29 are compact and may be disposed on the back of or inside the last television set in a series of rooms on either side of the hallway.

In a similar fashion the looped signal distribution system 23 comprises a voltage sensing switch 30 from which coaxial cables 31 and 32 lead through a plurality of devices 27 to termination points 33 and 34, respectively.

In operation, television RF signals are received by the antenna 11 and passed by the coaxial cable 12 through the RF/DC splitter 13 into the coaxial cable 15. The RF signals on the coaxial cable 15 are divided by the signal splitter 19 and are present on coaxial cables 20 and 21. Similarly, the signal on coaxial cable 20 is divided within the voltage sensing switch 24 and is present on the coaxial cables 25 and 26. In like manner the RF signals on coaxial cable 21 are divided within the voltage sensing switch and are present on the coaxial cables 31 and 32. In accordance with this invention, the coaxial cables 25, 26, 31, and 32 not only form the signal input to each of the devices or TV sets 27 but also have continuous loops of coaxial cable which extend through each of the devices 27 in a manner such that the loops can not be removed from the devices without either destroying the devices or cutting the coaxial cable loops. This may be simply done, for example, in the case of television sets by extending a continuous loop of coaxial cable through apertures in the chassi of the television set.

Referring now to the termination point or arrangement 28, the coaxial cable 25 is terminated by connecting it through a capacitor 35 to its characteristic impedance 36, which may be a 75 ohm resistor connected to ground. A voltage source 37 is also connected between ground and the coaxial cable 25 through an RF choke 38. The voltage source 37 may be a 6 volt source of DC or low frequency AC and its negative terminal is connected through the RF choke 38 to the coaxial cable 25 and its positive terminal is connected to ground. Likewise, the termination point 29 comprises a capacitor 39 and a resistor 40 for terminating the coaxial cable 26 in its characteristic impedance and a voltage source 41, which is connected through an RF choke 42, to the coaxial cable 26. The voltage source 41 is, however, oriented so that its positive terminal is connected through the RF choke 42 to the coaxial cable 26. Since the RF chokes 38 and 42 do not interfere with or impede DC or low frequency AC voltage, the coaxial cable 26 has a +6 volts appearing thereon, and the coaxial cable 25 has a 6 volts appearing thereon. The capacitors 35 and 39 isolate the termination impedances 36 and 40 respectively so that this DC or low frequency AC voltage does not appear across the impedances 36 and 40. The RF chokes 38 and 42 serve to isolate the voltage sources 37 and 41 from the RF signals on the coaxial cables 25 and 26.

In operation, as discussed before, complementary voltages appear on the coaxial cable distribution lines 25 and 26. That is, a 6 volts of either DC or low frequency AC appears on the coaxial cable 25 and a +6 volts DC or low frequency AC signal appears on the coaxial cable 26. The coaxial cables 25 and 26 are connected through the voltage sensing switch 24 to the coaxial cable 20. As will be discussed more fully hereinafter, the voltage sensing switch 24 senses the 6 volts on coaxial cable 25 and the +6 volts on coaxial cable 26 and as long as both these voltages are present at the inputs to the voltage sensing switch 24 there is no voltage output on the coaxial cable 20. When, however, one of the 6 or +6 voltages on coaxial cables 25 and 26, respectively, is removed, such as would happen, for example, if the loops extending into the television sets 27 are cut or short-circuited to ground, then" the voltage sensing switch 24 does produce a DC output on coaxial cable 20. This DC output on coaxial output 20 is passed through the signal splitter 19 and the' coaxial cable 15 to RF/DC splitter 13. Here the DC or low frequency AC voltage is blocked by the capacitor 14 from entering the coaxial cable 12 but passes through the RF choke l6 and conductor 17 into the voltage selective detector 18. The polarity and magnitude of this voltage is sensed by the voltage detector 18 so that an appropriate alarm light is lighted, indicating that an attempt is being made to steal one of the television sets 27 through which continuous loops of the coaxial cable 25 extend. The termination points 33 and 34 for the coaxial cables 31 and 32, respectively, are identical to the termination points 28 and 29 except that voltage sources 43 and 44 are utilized which are DC or low frequency AC voltages of 3 volts, with 3 volts being applied to the coaxial cable 31 and +3 volts being applied to the coaxial cable 32. These voltages are sensed in the voltage sensing switch 30 so that when either one of these voltages is not present there is a voltage output on the coaxial cable 21 which is passed through the signal splitter 19, coaxial cable 15 and RF/DC splitter 13 into the voltage selective detector 18. The voltage selector 18 is both polarity and magnitude sensitive so that with the arrangement shown in FIG. 1 different alarm lights are lighted depending upon whether the short circuit or open circuit of a coaxial cable is in coaxial cable 25, 26, 31 or 32. In accordance with this invention other looped signal distribution systems may be provided with different DC or low frequency AC voltages applied to the coaxial cable distribution lines contained therein.

Referring now to FIG. 2, there is shown an illustrative diagram in which the manner of extending continuous loops of coaxial cable through the plurality of devices or television sets 27 is shown. A coaxial cable, which may for example be the coaxial cable 26 of FIG. 1, extends into a wall plug 45 which may be fixed in place in a wall 46. The coaxial cable 25 extends through the wall plug 45 and is typically present at a connector socket in the wall plug 45. This socket is adapted to receive a plug which may be attached to a coaxial cable 47 for forming an RF signal input to the television set 27.

In accordance with this invention, a continuous loop of coaxial cable generally indicated by reference numeral 48 in FIG. 2 extends through the television set 27 in such a manner that this loop cannot be removed unless the television set 27 is destroyed or the coaxial cable of the loop 48 is cut. The coaxial cable in this loop 48 is spliced continuously into the coaxial cable 25. The coaxial cable then extends to the next television device 27 where it is connected to a wall plate having a female socket for receiving a coaxial cable signal conductor from the television set 27 and also has another continuous loop which goes through this other television set 27 for protecting it against theft.

The voltage sensing switches 24 and 30 are constructed in the same manner. Therefore, the details of only the voltage sensing switch 24 will be discussed and a detailed circuit diagram of the voltage sensing switch 24 is shown in FIG. 3. RF television signals, which may be present on the coaxial cable 20, are passed through a standard voltage-passing hybrid TV signal splitter 49. The television signal splitter 49 generally comprises windings 50, which are connected to the coaxial cable 20 and windings 51, which are inductively coupled to the windings 50 and are connected between terminals 52 and 53.

A resistor 54 is also connected between the terminals 52 and 53. Terminal 52 is connected through a capacitor 55 to the coaxial cable 26 and terminal 53 is connected through a capacitor 56 to the coaxial cable 25. The RF signals in windings 50 are coupled into the windings 51 and via terminal 52 and capacitor 55 into the coaxial cable 26 and via terminal 53 and capacitor 56 into the coaxial cable 25. A capacitor 109 provides an RF termination to ground for the windings 50 and 52.

The voltage sensing switch 24 also comprises an npn transistor 57 having base collector and emitter electrodes and a pnp transistor 58 also having base emitter and collector electrodes. The emitter of transistor 57 is connected through an RF choke 59 to terminal 52. The emitter of transistor 58 is connected through an RF choke 60 to terminal 53. The emitter of transistor 57 is also connected through a resistor 61 to ground and the emitter of transistor 58 is connected through a resistor 62 to ground. The collector of transistor 57 is connected through an RF choke 63 to the coaxial cable 26 and the collector of transistor 58 is connected through an RF choke 64 to the coaxial cable 25. The base of transistor 57 is connected through a resistor 65 to the collector of transistor 57 and is also connected through a resistor 66 to ground. Similarly the base of transistor 58 is connected through a resistor 67 through the collector of transistor 58 and is also connected through a resistor 68 to ground. The base of transistor 57 is also connected through a resistor 69 to the collector of transistor 58, and the base of transistor 58 is connected through a resistor 70 to the collector of transistor 57.

In operation, when there are no shorts or open circuits in the coaxial cables 25 and 26 coaxial cable 25 has a DC or low frequency AC voltage of -6 volts appearing thereon, and the coaxial cable 26 has a DC or low frequency AC voltage of +6 volts appearing thereon. The +6 volts on coaxial cable 26 is passed through the RF choke 63 and appears on the collector of transistor 57 and the 6 volts on coaxial cable 25 is passed through the RF choke 64 and appears on the collector of transistor 58.

Resistors 65, 66 and 61 provide forward biasing for the transistor 57 and resistors 68, 62 and 67 provide forward biasing for the transistor 58. However, the

negative voltage on the coaxial cable 25 is coupled through the RF choke 64 and resistor 69 to the base of transistor 57 and is normally effective to hold the transistor 57 in an off or non-conducting condition. Similarly the positive 6 volts on the coaxial cable 26 is coupled through the RF choke 63 and the resistor to the base of the transistor 58 and is normally effective to hold the transistor 58 in an off or non-conducting condition. However, if the -6 volts disappear from the coaxial cable 25, which would happen if the coaxial cable 25 were short-circuited or open-circuited, then the voltage on the base of transistor 57 rises and transistor 57 is turned on and begins conducting. If transistor 57 turns on its emitter is raised to the +6 volts present on coaxial cable 26 and this voltage is coupled through the RF choke 59 across the resistor 54. This voltage across resistor 54 also appears across the windings 51 and is coupled into the windings 50 so that a +6 volts of DC or low frequency AC appears on the coaxial cable 20.

In a similar manner, the +6 volts present on coaxial cable 26 is coupled through RF choke 63 and resistor 70 to the base of transistor 58, and is normally effective to hold the transistor 58 off or in a non-conducting state. When, however, the +6 volts on coaxial cable 26 is removed, as might happen when the coaxial cable 26 is short-circuited or open-circuited, the voltage on the base of transistor 58 falls, turning transistor 58 on. When transistor 58 turns on, its emitter is raised to the voltage of the coaxial cable 25, which in this instance is -6 volts, and this voltage is coupled through the RF choke 60 across the resistor 54. This voltage appearing across resistor 54 also appears across the winding 51 and is coupled into the winding 50, so that a 6 volts appears on the coaxial cable 20. Thus, when the coaxial cable 26 is short-circuited or open-circuited a DC voltage of -6 volts appears on the coaxial cable 20. Similarly, when the coaxial cable 25 is short-circuited or open-circuited a positive 6 volt DC voltage appears upon the coaxial cable 20.

Turning now to a consideration of FIG. 4, there is shown a detailed circuit diagram of the voltage selective detector of FIG. 1. The voltage selective detector 18 is adapted to receive through conductor 17 the DC or low frequency AC voltages which are passed by any of the voltage sensing switches in response to a short circuit or open circuit of one of the coaxial cable distribution lines. The voltage selective detector 18 comprises a series of silicon controlled switches so connected that they are activated or made conductive when specific preselected voltages of positive or negative polarity are applied to the gate portion of these silicon controlled switches. For example, assuming that the theft alarm system has four coaxial cable distribution lines with voltages of +6 and 6 volts applied to two of these distribution lines and +3 and 3 volts applied to the other two of these distribution lines, then four silicon controlled switches are required in the voltage selective detector 18. These four silicon controlled switches 71 through 74 are shown in FIG. 4 and each of the switches has an anode electrode, a cathode electrode, an anode gate and a cathode gate electrode. The cathodes of all of the silicon controlled switches 71 through 74 are connected to ground. The anode of silicon controlled switch 71 is connected through a lamp 106 to a conductor 75. A transistor 76 is provided having base collector and emitter electrodes. The emitter electrode of transistor 76 is connected to the anode of the silicon controlled switch 72 and the collector electrode of transistor 76 is connected through a lamp 77 to the conductor 75. The anode of silicon controlled switch 73 is connected through a lamp 78 to the conductor 75. Another transistor 79 is provided having base collector and emitter electrodes. The emitter of transistor 79 is connected to the anode of silicon controlled switch 74 and the collector of transistor 79 is connected through a lamp 80 to the conductor 75. An alarm 81 which may be an audible alarm, for example, and a re-set switch 82 are connected in series between a source of voltage 83 and the conductor 75. An alarm silence switch 84 is also connected across the alarm 81 in parallel therewith.

Assume first of all that a positive 3 volts appears on the conductor- 17. This positive 3 volts is coupled through a diode 85 and a resistance-capacitance network comprising resistors 86 and 87 and a capacitor 88 to the cathode gate of the silicon controlled switch 72. A positive voltage also appears at the base of the transistor 76 due to conduction from the voltage source 83 through the resistors 89 and 90 to ground so that the transistor 76 is conducting. This positive 3 volts builds up across the capacitor 88 so that the silicon controlled switch 72 is turned on through its cathode gate. When this happens the lamp 77 is essentially connected between the conductor 75 and ground so that lamp 77 is lighted and the alarm 81 is actuated due to conduction in conductor 75. This gives an indication that a theft is being attempted of one of the devices such as television sets connected in the distribution line which corresponds to a positive 3 volts on the conductor 17. The positive 3 volts on the conductor 17 is also applied through a diode 91 anda resistance-capacitance network comprising resistors 92 and 93 and capacitor 94 to the cathode gate of the silicon controlled switch 71. The values of the resistance-capacitance network comprising resistors 92 and 93 and capacitor 94 are selected such that the silicon control switch 71 will not conduct in response to a positive 3 volts but requires a higher voltage, such as a positive 6 volts for example. The diodes 95 and 96 prevent application of the positive 3 volts to silicon control switches 73 and 74.

Now let it be assumed that a positive 6 volts appears on the conductor 17 corresponding to a short circuit or open circuit in a different one of the coaxial cable distribution lines. This positive 6 volts is applied through diode 85 and a resistance-capacitancenetwork comprising resistors 86 and 87 and capacitor 88 to the cathode gate of the silicon controlled switch 72 and is also-applied through the diode 91 and the resistancecapacitance network comprising resistors 92 and 93 and capacitor 94 to the cathode gate of the silicon controlled switch 71. A positive 6 volts is sufficient to cause both silicon controlled switch 7l and silicon controlled switch 72 to be turned on. When, however, the silicon controlled switch 71 turns on its anode goes to essentially ground potential. Since its anode is connected through the resistor 89 to the base of the transistor 76, the potential on the base of transistor 76 falls, serving .to turn the transistor 76 off. With the transistor 76 off, there can be no conduction through the silicon controlled switch 72 and the lamp 77 is not lighted. However, the lamp 106 is lighted since the silicon controlled switch 71 is conducting and as before the alarm 81 is actuated. The lighting of lamp 106 gives an indication that a theft is being attempted of a television set which is connected in another one of the coaxial cable distribution lines which corresponds to a positive 6 volts appearing on the conductor 17. The alarm 81 may be silenced by closing the alarm silence switch 84 which short circuits the alarm 81. The whole alarm system may be re-set by temporarily opening the re-set switch 82 so as to remove the voltage source 83 from connection to the anodes of silicon controlled switches 71 through 74.

Now let it be assumed that a negative 3 volts appears on the conductor 17. Diode and 91 prevent the application of this negative 3 volts to either of these silicon control switches 71 or 72. The negative 3 volts, however, is coupled through a diode 107 and a resistance-capacitance network comprising resistor and 96 and the capacitor 97 to the anode gate of the silicon controlled switch 74. Similarly, the negative 3 volts is coupled through a diode 108 and a resistancecapacitance network comprising resistor 98 and 99 and a capacitor 100 to the anode gate of the silicon controlled switch 73. The cathode gate of silicon controlled switch 74 is connected through a capacitor 101 to ground and the cathode gate of the silicon controlled switch 73 is connected through a capacitor 102 to ground.

Normally, the transistor 79 is conducting since it is forward biased and has a positive potential at its base due to conduction through resistors 103 and 104 to ground. Application of the negative 3 volts to the resistance-capacitance network comprising resistors 95 and 96 and the capacitor 97 builds up a negative 3 volt charge across the capacitor 97 which is sufficient to turn on the silicon controlled switch 74. Since the transistor 79 is also conducting the lamp 80 will be lighted. The values of the resistors 98 and 99 and the capacitor 100, which are associated with the anode gate of the silicon controlled switch 73, are selected such that a negative 3 volts on the conductor 17 is not sufficient to turn on the silicon controlled switch 73.

Now let it be assumed that a negative 6 volts is applied to the conductor 17. This negative 6 volts is coupled through diode 107 and resistance-capacitance network comprising resistors 95 and 96 and the capacitor 97 to the anode gate of the silicon control switch 74 and is of a high enough value to turn on the silicon controlled switch 74. However, the negative 6 volts is also coupled through the diode 108 and the resistance capacitance network comprising resistors 98 and 99 and the capacitor 100 to the anode gate of the silicon controlled switch 73. The negative 6 volts builds up across the capacitor 100 and is sufficient to turn on the silicon controlled switch 73. When silicon control switch 73 turns on its anode essentially goes to ground so that the lamp 78 is lighted. The base of transistor 79 is also connected through a resistor 103 to the anode of the silicone controlled switch 73. When silicon control switch 73 turns on and its cathode goes to ground the base of transistor 79 also goes to ground and transistor 79 is turned off. With transistor 79 turned off there can be no conduction through the silicon controlled switch 74 so that the lamp 80 is not lighted.

If more than 4 coaxial cable distribution lines are utilized in the hotel or motel in which it is desired to install this theft alarm system then, as was discussed previously, more voltage sensing switches are necessary and voltage sources having different DC or low frequency AC voltages are necessary to be applied to these additional coaxial distribution lines at their termination points. For example, +9 and 9 volts and +12 and l 2 volts could also be utilized. In this situation the voltage selective detector 18, as was shown and described in FIG. 4, would also include additional silicon controlled switches adapted to be actuated only upon application of +9 or -9 volts or +12 or l2 volts as the case may be. Circuitry would be similar to that shown in FIG. 4, and the manner in which to connect this additional circuitry should be obvious to those skilled in the art.

Iclaim:

1. In a signal distribution system including an antenna system for receiving signals, a plurality of remote devices each having a signal input, and a signal distribution system for distributing the signals received by the antenna system to the signal inputs of the plurality of remote devices by means of a plurality of signal distribution lines extending between the antenna system and termination points with the signal inputs of a number of the remote devices connected to each of the signal distribution lines, a theft alarm system comprising continuous loops of a signal distribution line extending respectively through each of the remote devices having signal inputs connected to that signal distribution line in a manner such that a loop cannot be removed without destroying the device or cutting the continuous loop of signal distribution line, voltage source means attached to the termination point of each of the signal distribution lines for applying a voltage to each of the signal distribution lines which voltage does not interfere with transmission of signals from the antenna system along the signal distribution lines, voltage sensing means connected to each of the signal distribution lines for detecting the voltage thereon, said voltage sensing means adapted to generate an alarm in response to a change in value of said voltage on a signal distribution line which occurs when the signal distribution line is open-circuited or short-circuited.

2. In a signal distribution system including an antenna system for receiving signals, a plurality of remote devices each having a signal input, and a signal distribution system for distributing the signals received by the antenna system to the signal inputs of the plurality of remote devices by means of a plurality of signal distribution lines extending between the antenna system and termination points with the signal inputs of a number of the remote devices connected to each of the signal distribution lines, a theft alarm system comprising continuous loops of a signal distribution line extending through each of the remote devices having signal inputs connected to that signal distribution line in a manner such that a loop cannot be removed without destroying the device or cutting the continuous loop of signal distribution line, voltage source means in each of the signal distribution lines for applying a voltage to each of the signal distribution lines which does not interfere with transmission of signals from the antenna system along the signal distribution lines, voltage sensing means connected to each of the signal distribution lines for detecting the voltage thereon, said voltage sensing means'comprising a plurality of voltage sensing switches, a voltage selective detector and an alarm, each of said voltage sensing switches having two inputs and an output, each of said voltage sensing switch inputs coupled to a signal distribution line, each of said voltage sensing switch outputs coupled to said voltage selective detector and adapted to generate a voltage output in response to open or short-circuitring of any of said signal distribution lines coupled to said voltage sensing switch, said voltage selective detector responsive to said voltage output to actuate said alarm.

3. The theft alarm system of claim 2 wherein the magnitude and polarity of said voltage output is indicative of which of said signal distribution lines is open or short-circuited and wherein said voltage selective detector actuates different alarms depending upon the magnitude and polarity of said voltage output.

4. The theft alarm system of claim 2 wherein said voltage source means coupled to said signal distribution lines which form said two inputs to a particular one of said voltage sensing switches comprises two complementary voltage sources for applying complementary voltages to said signal distribution lines.

5. The theft alarm system of claim 4 wherein each of said voltage sensing switches comprises a pair of complementary transistors each having an input and having a common output, said transistor inputs respectively coupled to said complementary voltage sources over said signal distribution lines, each of said pair of complementary transistors normally biased off by said complementary voltage source connected to said input but adapted to be biased on and generate said voltage output in response to open or short-circuiting of said signal distribution line whereby said complementary voltage source is no longer coupled to said input.

6. The theft alarm system of claim 3 wherein said voltage selective detector comprises a plurality of silicon controlled switches, one for each of said signal distribution lines, each said silicon controlled switch having an alarm actuated in response to conduction of said silicon controlled switch, each said silicon controlled switch having an input and a resistance-capacitance network for connecting said input to said voltage output, each of said silicon controlled switches adapted to conduct in response to voltage of a particular magnitude and polarity of said voltage output.

7. In a signal distribution system including an antenna system for receiving signals, a plurality of remote devices each having a signal input, and a signal distribution system for distributing the signals received by the antenna system to the signal inputs of the plurality of remote devices by means of a plurality of signal distribution lines extending between the antenna system and termination points with the signal inputs of a number of the remote devices connected to each of the signal distribution lines, a theft alarm system comprising continuous loops of a signal distribution line extending respectively through each of the remote devices having signal inputs connected to that signal distribution line in a manner such that a loop cannot be removed without destroying the device or cutting the continuous loop of signal distribution line, voltage source means in each of the signal distribution lines for applying a voltage to each of the signal distribution generate an alarm in response to a change in value of said voltage on a signal distribution line which occurs when the signal distribution line is open-circuited or short-circuited. 

1. In a signal distribution system including an antenna system for receiving signals, a plurality of remote devices each having a signal input, and a signal distribution system for distributing the signals received by the antenna system to the signal inputs of the plurality of remote devices by means of a plurality of signal distribution lines extending between the antenna system and termination points with the signal inputs of a number of the remote devices connected to each of the signal distribution lines, a theft alarm system comprising continuous loops of a signal distribution line extending respectively through each of the remote devices having signal inputs connected to that signal distribution line in a manner such that a loop cannot be removed without destroying the device or cutting the continuous loop of signal distribution line, voltage source means attached to the termination point of each of the signal distribution lines for applying a voltage to each of the signal distribution lines which voltage does not interfere with transmission of signals from the antenna system along the signal distribution lines, voltage sensing means connected to each of the signal distribution lines for detecting the voltage thereon, said voltage sensing means adapted to generate an alarm in response to a change in value of said voltage on a signal distribution line which occurs when the signal distribution line is open-circuited or short-circuited.
 2. In a signal distribution system including an antenna system for receiving signals, a plurality of remote devices each having a signal input, and a signal distribution system for distributing the signals received by the antenna system to the signal inputs of the plurality of remote devices by means of a plurality of signal distribution lines extending between the antenna system and termination points with the signal inputs of a number of the remote devices connected to each of the signal distribution lines, a theft alarm system comprising continuous loops of a signal distribution line extending through each of the remote devices having signal inputs connected to that signal distribution line in a manner such that a loop cannot be removed without destroying the device or cutting the continuous loop of signal distribution line, voltage source means in each of the signal distribution lines for applying a voltage to each of the signal distribution lines which does not interfere with transmission of signals from the antenna system along the signal distribution lines, voltage sensing means connected to each of the signal distribution lines for detecting the voltage thereon, said voltage sensing means comprising a plurality of voltage sensing switches, a voltage selective detector and an alarm, each of said voltage sensing switches having two inputs and an output, each of said voltage sensing switch inputs coupled to a signal distribution line, each of said voltage sensing switch outputs coupled to said voltage selective detector and adapted to generate a voltage output in response to open or short-circuitring of any of said signal distribution lines coupled to said voltage sensing switch, said voltage selective detector responsive to said voltage output to actuate said alarm.
 3. The theft alarm system of claim 2 wherein the magnitude and polarity of said voltage output is indicative of which of said signal distribution lines is open or short-circuited and wherein said voltage selective detector actuates different alarms depending upon the magnitude and polarity of said voltage output.
 4. The theft alarm system of claim 2 wherein said voltage source means coupled to said signal distribution lines which form said two inputs to a particular one of said voltage sensing switches comprises two complementary voltage sources for applying complementary voltages to said signal distribution lines.
 5. The theft alarm system of claim 4 wherein each of said voltage sensing switches comprises a pair of complementary transistors each having an input and having a common output, said transistor inputs respectively coupled to said complementary voltage sources over said signal distribution lines, each of said pair of complementary transistors normally biased off by said complementary voltage source connected to said input but adapted to be biased on and generate said voltage output in response to open or short-circuiting of said signal distribution line whereby said complementary voltage source is no longer coupled to said input.
 6. The theft alarm system of claim 3 wherein said voltage selective detector comprises a plurality of silicon controlled switches, one for each of said signal distribution lines, each said silicon controlled switch having an alarm actuated in response to conduction of said silicon controlled switch, each said silicon controlled switch having an input and a resistance-capacitance network for connecting said input to said voltage output, each of said silicon controlled switches adapted to conduct in response to voltage of a particular magnitude and polarity of said voltage output.
 7. In a signal distribution system including an antenna system for receiving signals, a plurality of remote devices each having a signal input, and a signal distribution system for distributing the signals received by the antenna system to the signal inputs of the plurality of remote devices by means of a plurality of signal distribution lines extending between the antenna system and termination points with the signal inputs of a number of the remote devices connected to each of the signal distribution lines, a theft alarm system comprising continuous loops of a signal distribution line extending respectively through each of the remote devices having signal inputs connected to that signal distribution line in a manner such that a loop cannot be removed without destroying the device or cutting the continuous loop of signal distribution line, voltage source means in each of the signal distribution lines for applying a voltage to each of the signal distribution lines which voltage does not interfEre with transmission of signals from the antenna system along the signal distribution lines, voltage sensing means connected to each of the signal distribution lines for detecting the voltage thereon, said voltage sensing means adapted to generate an alarm in response to a change in value of said voltage on a signal distribution line which occurs when the signal distribution line is open-circuited or short-circuited. 